1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery and a battery pack.
2. Description of the Related Art
A non-aqueous electrolyte battery that effects charging/discharging through the movement of lithium ions between a negative electrode and a positive electrode is intensively studied and developed as a high energy density battery.
The non-aqueous electrolyte battery is demanded to have various properties depending on the end-use thereof. For example, if it is desired to be used as a power source for a digital camera, the battery is required to exhibit the discharging of about 3 C. Whereas, if it is desired to be used as a power source for vehicles such as a hybrid electric motor car, the battery is expected to require the discharging of about 10 C or more. For this reason, the non-aqueous electrolyte battery to be used for these end-uses is desired to exhibit especially large current characteristics.
In the non-aqueous electrolyte battery available in the market, lithium-transition metal composite oxides are employed as an active material of the positive electrode and carbonaceous materials are employed as an active material of the negative electrode. As for the transition metals included in the lithium-transition metal composite oxides, metals such as Co, Mn, Ni, are generally employed.
In recent years, there is concern about the degradation in safety of the non-aqueous electrolyte battery, attributable to improvements for higher output power, higher energy density and higher capacity.
With respect to the safety of the non-aqueous electrolyte, internal short-circuit caused by contamination with electroconductive foreign substances in a production process of the batteries cannot be prevented by an external circuit (protection circuit) devised to prevent over charging/over discharging. Therefore, this problem should be coped with by the battery itself.
Accordingly, JP-A 2005-183179 (KOKAI) discloses a battery wherein an inorganic insulating material layer such as an alumina layer is formed on the surface of a negative electrode containing a carbonaceous material as an active material to improve safety at the time of internal short-circuit.
In the invention disclosed in the above document, however, the inorganic insulating material layer such as an alumina layer formed on the surface of the negative electrode is highly resistive and functions as a resistance component against the negative electrode regardless of a charging/discharging state, thus degrading the large-current performance of the battery.